In 1982 K. Eric Drexler introduced the idea of assemblers of molecular size in his book “Engines of Creation” (cited above). Nanotechnology is the subject of at least one international conference, and one commercial venture has been organized and funded to invest research and planning in this technology. Although commercial realization of nanotechnology may be years away, there is strong indication that research following the human genome project, and particularly the study of protein structure and function, will require tools to manipulate components of the cell. Development of these tools is a demanding, exciting, and challenging research subject.
Miniaturization of mechanical devices is evolving toward nanometer scale, requiring handling and assembly of objects as small as a few nanometers. Manipulation of samples and specimens smaller than a few microns in size demands a technology that, at present, does not exist. Assemblers are needed that can grip collections of molecules, releasing them from their present location, lifting, rotating, and forcefully placing them in a new environment.
Existing micropositioners do not provide the requisite flexibility of motion for assembly tasks that are contemplated. Forceful shape memory alloy actuators can be scaled to micron size. These devices are thermally powered and so require a source of heat energy: this heat may be supplied by conduction, joule heating, infrared light, or other means. The present invention contemplates the use of a scanning electron microscope beam to provide heat energy to energize thermal actuators. Prototype actuators are fabricated by sputter deposition of titanium-nickel thin film, photolithographic patterning, and chemical milling. A scanning electron beam is positioned to produce local heating, and to observe the resulting motion.
Atomic force microscopy can be used to move individual atoms but not to grip larger objects with enough force to hold against local forces. In recent investigations of the properties of carbon nanotubes, piezoelectric stepper motors have been used to manipulate structures orders of magnitude smaller than the drivers (see MF Yu et al. in “3 Dimensional Manipulation of Carbon Nanotubes under a Scanning Electron Microscope”). Manipulation of objects this small would be improved if the end-effectors were not much larger than the objects they control. In analogy to the shoulder-wrist-finger arrangement of the human hand, gross positioning should be managed by actuators of macroscopic size, and fine control by end-effectors of much smaller size.
The force of actuation should be produced as close as possible to the point of application. This implies that manipulation of sub-micron size objects requires micron-size actuators. Conventional actuators (electromagnetic, piezoelectric) do not scale well to micron size. A promising form of actuation is heat-actuated devices, particularly shape memory actuators. Photolithography provides means of fabricating devices of sub-micron size. Miniature shape memory alloy (SMA) actuators rely on joule heating to cause the phase change. In the sub-micron range it is difficult to make electrical connection, especially on devices that move. To solve this problem, the present invention focuses on the actuation of sub-micron scale shape memory alloy devices by electron-beam excitation.
The present invention is directed to the operation of microactuators by focused beam energy. Whereas microactuators now require wires or tubes attached to get the energy and control signals down to them, this invention discloses a wireless technique for both control and energy, as well as the return path for observation and data.
Current devices are fabricated as small as a few hundred microns using conventional microlithography. Shrinking this technology to sub-micron dimensions has raised at least two questions: (i) Will the shape memory property be preserved when the dimensions are as small or smaller than the crystal domains? And (ii)
How can such small objects (sub-micron) be selectively heated to produce actuation? The present invention, based upon research conducted to answer such questions, provides preliminary proof-of-concept.
In accordance with the present invention, there is provided a method for driving a shape memory alloy actuator, including the steps of: pre-straining a shape memory alloy in its low-temperature state; and subsequently, heating the shape memory alloy above its phase transformation temperature using a focused beam.
One aspect of the invention is based on the discovery of techniques for achieving high work output per unit volume in micro-robotic actuators, and in particular TiNi and similar actuators. Such actuators are attractive as a means of powering nano-robotic movement, and are sitable for manipulation of structures at or near the molecular scale. In these very small devices (one micron scale), one means of delivery of energy is by electron beams. Movement of mechanical structures a few microns in extent has been demonstrated in a scanning electron microscope. Results of these and subsequent experiments will be described, with a description of potential structures for fabricating moving a microscopic x-y stage.
The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.